RELATIONSHIP BETWEEN CR AND BREATHING PATTERN IN MECHANICALLY VENTILATED PATIENTS

In mechanically ventilated patients the natural gas-conditioning proce ss of the upper airways is bypassed by the use of an endotracheal tube or a tracheostomy. We hypothesized that under these conditions the br eathing pattern may greatly influence the convective respiratory heat loss (Cr). Cr values were computed from minute ventilation (VE) and in spiratory and expiratory gas temperatures, which were measured in six patients under mechanical ventilation for the management of cranial tr auma. In each patient the effects of 11-20 different breathing pattern s were investigated. Relationships between Cr and VE and between combi ned tidal volume and respiratory frequency were obtained by simple and multiple linear regression methods, respectively. Comparison of the s tandard errors of estimate indicated that multiple linear regression g ives the best fit. Thus, Cr was highly dependent on the breathing patt ern and was not related only to VE. For the same VE value, Cr was high er when VE was achieved with high tidal volume and low respiratory fre quency. These data are consistent with previous studies in which therm al exchanges through the upper airways were taxed by hyperventilation of frigid air.